Numerous artificial hearts and blood pumps have been devised to replace a defective or diseased heart and closely simulate the functioning of a healthy, natural heart. In contrast to heart transplantation, which requires a donor and involves serious rejection problems, a total artificial heart may be mass-produced and is potentially more compatible with the host's immune system. However, an artificial heart must be compact enough to fit in the chest cavity, and must consistently maintain proper blood flow based on the host's level of activity. The input and output flow characteristics of the artificial heart must be sufficient to protect the blood cells from hemolysis (dissolution) and thrombosis (clotting). The artificial heart mechanism must also be extremely reliable and durable.
One example of an artificial heart is disclosed in U.S. Pat. No. 3,152,340 issued Oct. 13, 1964 to Fry, et al. In this device, a piston and plate assembly is positioned between two diaphragms, or imitation heart chambers. A motor mounted above the chambers delivers a driving force to the piston and plate assembly and, in turn, to the diaphragms through an eccentric looped pitman for alternatively exhausting the chambers via back-and-forth movement of the piston and plate assembly. Flow into and out of the inlets and outlets is regulated by a set of floating plate valves located outside the inlets and outlets on respective valve boxes located laterally of the diaphragms.
U.S. Pat. No. 4,512,276 issued Apr. 23, 1985 to Strimling discloses another artificial heart having three pump chambers separated by a pair of diaphragms in contact with cooperating cam-equipped pusher plates. A variable length rod connects the pusher plates and holds a rotary electric motor carrying rollers which move the pusher plates by actuating the cams provided on each of the pusher plates to alternatively contact the diaphragms and effectuate pumping.
U.S. Pat. No. 4,820,300 issued Apr. 11, 1989 to Pierce, et al shows a further artificial heart which utilizes a fluid displaced from a left blood pump to power a right blood pump. The left blood pump is a sac-type pump powered by an electric motor that, when contracting or expanding, displaces a volume of fluid in a chamber within the left pump housing. The fluid is displaced through a fluid line connecting the right blood pump, which is a pneumatically operated sac-type or rotary-type pump.
Another artificial heart described in "An Artificial Heart For Clinical Use", Annals of Surgery, Sept. 1990, pp. 339-343 employs a pusher plate assembly between a pair of bladders for alternatively compressing each bladder by reciprocal movement of the pusher plate assembly. In a first version, a cam-type electric motor positioned between the bladders provides the driving force to reciprocate the pusher plate assembly. In a second version, a roller screw-type electric motor disposed intermediate the bladders transmits back-and-forth motion to the pusher plate assembly.
These known arrangements are generally deficient in meeting one or more of the requisites discussed above, and a need remains for a compact, reliable artificial heart which enables proper circulation of blood in the body.